1. Field of the Invention
The present invention relates to a power transfer device for four-wheel drive, and more particularly to an improvement of an output shaft assembly in the power transfer device.
2. Description of the Background
In U.S. Pat. No. 4,643,045 granted to Katayama on Feb. 17, 1987, there has been proposed a power transfer device for four-wheel drive in combination with a power transmission, wherein a ring gear is rotatably mounted on a lateral shaft in a casing of the transfer device to be applied with driving power from the power transmission through an intermediate or center differential gear unit, and wherein an output shaft is rotatably mounted within the casing and arranged in a fore-and-aft direction of the vehicle to transmit the driving power from the ring gear to a propeller shaft for rear-wheel drive. The output shaft is supported by a pair of axially spaced bearings carried on the casing and has an input end portion integral with a drive pinion meshed with the ring gear and an externally splined output end portion for drive connection to the propeller shaft. In such a structure as described above, the output shaft must be elongated for drive connection to the propeller shaft and enlarged in diameter to ensure sufficient rigidity of the externally splined output end portion, while the casing must be enlarged and thickened in its peripheral wall to support thereon the externally splined output end portion of the output shaft. For this reason, the power transfer device becomes heavy and large in size.